Posi break in

[buck91]

The short version is this: Installed an Eaton Posi in my truck this fall about 500 miles ago. After A LOT of research I opted for Motorcraft 75w140 oil with 4oz of Motorcraft FM. Was experiencing heavy clutch chatter, so just this week I finally added another 4oz of FM. Eaton tech support had recommended starting with 4oz and titrating up while the pdf owners manual states start with 1.5oz of FM per quart of oil.

Anyways, when adding the FM the diff was very full and leaked oil out of the fill plug, so I suction gunned about 10oz out before adding the FM (and of course squirted the oil back in). Anyways, what I noticed was interesting. The gear oil had turned QUITE dark, much darker than even the original with 80k miles on it was. With little grey particles in suspension. The magnet had a few pieces of metal stuck to it, but nothing concerning. I suspect this fluid color was due to posi break in of mostly the clutches, as well as the spiders and I also have new carrier bearings at the same time.

As far as break in oil, all the info I can find really relates that to replacing the r&p, and nobody really talks about if you replace just the carrier bearing and diff. Even the Eaton instructions omit any mention of break-in oil change.

I'm 100% sure that dropping the fluid and replacing won't hurt, of course... but I have a busy life and could go without the extra task and extra cost. Can anybody present reasons or an argument which would actually support leaving the gear oil in there? I would love to do that

 

[Ducman]

I assume the work was clean during the process.
One spec of dirt introduced into the housing can potentially wreak havoc in there.
Assuming all is well.
At 500 Miles it's not unreasonable to expect to do an oil change a little early in the interests of getting the initial break-in material out and maximizing the life of the unit.
The Diff chatter you have been having inevitably generates more wear and tear than normal.

Personally I normally do my first oil change at about 800-1000 Kms.
Then another oil change somewhere around the 20,000-30,000 km mark.
After this, the oil life can almost be expected to be many 10's of thousands of Kms provided the unit is not used in an overdriven capacity/duty cycle.
The initial wear metals generated will taper off dramatically and progressively after the initial oil change. Experience has shown this trend to be the case and is also verified by Oil analysis.

Should you go ahead with the oil change, I would highly recommend starting off with the full 4oz dosage of Limited Slip additive and leaving the oil level down 3-6mm from the bottom of the filler hole.
That way you can add the Limited Slip additive as required, then have some scope to top up the oil at your earliest convenience.
Even if the oil level it's down a little, it shouldn't hurt anything at all in the short term.

 

[4WD]

Do you have to pull the pumpkin cover to change oil ... ?

 

[meborder]

I would probably change it.

But, OTOH, ford recommends a 150k service interval even on the axles equipped with TracLoc.

In days gone by, a 15k fluid change was the norm for any clutch type limited slip, presumably for the reasons you mention.

Food for thought....